共查询到19条相似文献,搜索用时 406 毫秒
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一种新颖的超宽带无线通信多址接入方式的研究 总被引:2,自引:0,他引:2
多址干扰是限制超宽带(UWB)系统容量的主要原因。本文介绍了一种混合式多址接入方案:即采用直接序列扩频与固定跳时扩频相结合的多址接入机制,称之为DS-BPSK/固定THMA)。由于固定跳时码的存在,不同用户脉冲的碰撞概率被有效地减小。同时,即使发生脉冲碰撞,利用代表数据符号的直接序列PN码良好的自相关和互相关特性,将进一步抑制多址干扰影响。性能分析和仿真结果表明DS-BPSK/固定TH的UWB系统比传统的通过脉冲调制实现的跳时多址接入UWB系统具有更大用户容量。 相似文献
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随着互联网终端海量接入,传统正交多址接入(orthogonal multiple access,OMA)技术接入效率低, 5G NR 系统面临拥塞及高时延问题,并且在高速场景下,基于正交频分复用(orthogonal frequency-division multiplexing,OFDM)的系统由于多普勒效应性能严重恶化。为满足6G在高速移动场景下低时延、高可靠、海量接入需求,首先,结合正交时频空间(orthogonal time frequency space,OTFS)和图样分割多址接入(pattern division multiple access,PDMA)技术,提出了一种OTFS-PDMA联合方案;然后,推导PDMA传输码字在时延-多普勒(delay-Doppler,DD)域采用不同分配方式的系统输入-输出关系;最后,提出了一种基于期望传播算法(expectation propagation algorithm,EPA)的低复杂度接收机。仿真结果表明,OTFS-PDMA较传统的OTFS-OMA技术能够显著提升误码率性能;对于规则码本,不同码字分配方案性能相似,而对于非规则码本,发送信号采用集中式扩频优于离散式扩频,且对于离散式扩频,PDMA 扩频信号沿多普勒轴分配,系统可取得较好性能;此外EPA接收机性能优于其他传统接收机。 相似文献
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一种新的跳时多址DCSK系统设计与分析 总被引:1,自引:0,他引:1
常见差分混沌键控(DCSK)系统的多址方案存在两个问题,首先所有用户共享同一时隙,只能利用混沌信号的低互相关性来降低多址干扰。其次发送的参考信号和数据信号并不相同或相反,破坏了DCSK系统的良好抗多径性。该文提出了DCSK系统一种新颖的跳时多址方式。该方式给每个用户分配不同的伪随机跳时码,根据跳时码参考信号和数据信号进行相同量的跳时。从理论上给出了多址系统在加性高斯白噪声信道中的误码率解析式。分析和仿真表明该跳时多址方式可以很好地解决上述两个问题,而且具有更低的误码率。 相似文献
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基于扩频与跳频的多带OFDM-UWB多址技术 总被引:1,自引:0,他引:1
根据多带OFDM-UWB通信系统的特点,提出一种基于扩频与跳频的多址技术。该多址技术将多载波码分多址和跳频多址相结合,构成一种新颖的多址技术-正交频分多址(OFDMA),实现多载波码分多址技术和跳频多址技术的优势互补,此接收机的复杂性明显小于常规时频码的多用户接收机。仿真结果表明,基于OFDMA多址技术方案的UWB系统在系统误比特率性能上优于常规时频码方案约5dB。 相似文献
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针对60 GHz脉冲无线通信系统中存在的多址接入干扰问题,研究了基于FTH-PPM多址接入方案的性能。在IEEE 802.15.3c信道模型下,分析了系统误码率性能与跳频码数量、信噪比、用户数之间的关系,研究了FTH-PPM多址调制系统特性,并与TH-PPM、TH-PAM方案进行比较。仿真结果表明,系统在多址条件下,可以通过改变信噪比、频率跳数、用户数来满足所需的误码率,同时在一定范围内,FTH-PPM的误码率性能优于TH-PAM和TH-PPM的误码率性能,并且可以根据脉冲占空比的值选择合适的多址调制方式,为60 GHz脉冲无线通信的应用提供技术参考。 相似文献
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针对传统混沌映射迭代生成的时间序列复杂度低且序列取值范围受映射参数控制的问题,提出了一种基于S-T耦合级联混沌映射的扩频码生成算法。先通过引入耦合控制因子对满映射条件下的Sine映射和Tent映射进行线性耦合,在保持系统动力学结构完整性的前提下减弱了混沌参数取值对序列取值范围带来的影响,极大地增加了扩频码的地址空间。进一步,继续将耦合映射与Sine映射级联后作为扩频码生成器的驱动内核,通过级联的方式显著提升了映射迭代生成时间序列的复杂度,使得所生成的扩频码具有更强的伪随机特性。最后,基于Simulink平台搭建了加载S-T混沌扩频码的直序扩频系统,测试了在不同噪声环境下系统的误码率。实验结果表明,与基于原有传统映射的扩频系统相比较,基于线性耦合级联映射的扩频系统具有更低的误码率。 相似文献
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用于跳频多址通信的混沌跳频码 总被引:34,自引:3,他引:31
跳频码的性能对跳频多址通信起着关键性作用。设计具有良好汉明相关和随机性且数量多的跳频码是非常重要的。本文提出一种利用由混沌映射描述的离散混沌系统设计跳频码的新方法。首先由混沌映射产生混沌时间序列,然后利用量化技术对混沌时间序列进行量化,最后由量化后的混沌时间序列产生伪随机跳频码。为了增大混沌跳频码的周期和非线性复杂度,我们利用多个不同混沌映射组成一个级联混沌映射,并用来设计跳频码。实验表明,混沌跳频码具有非常好的性能。 相似文献
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Cheng-bing HE Shao-jing JING Fei HUA Rui XI Rui-yu ZHANG Wen-tao SHI Qun-fei ZHANG 《通信学报》2017,38(7):11-17
Aiming at the problem of low data rate and high receiver complexity of existing direct sequence spread spectrum code division multiple access (DS-CDMA),a novel code division multiple access (CDMA) using cyclic shift keying (CSK) signaling,namely CSK-CDMA,was proposed for multiuser underwater acoustic communication.The proposed method used the cyclic correlation characteristic of spread spectrum signals with M-ary modulation to provide a higher data rate than conventional.Passive time reversal technology was employed to suppress inter-code interference between users and the co-channel interference.The quasi-orthogonality of spread spectrum code was used to improve the processing gain.Multiuser communications are demonstrated with lake experimental recorded data under the condition of 5.27 km distance and complex multipath interference.The data rate is 39 bit/s/user for 6 users with bit error rate around 10-2~10-4. 相似文献
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The performance of asynchronous time-hopping ultra-wideband (TH-UWB) multiple access spread spectrum is analytically investigated in a UWB realistic multipath channel and in the presence of narrowband interference (NBI). In particular, an interference suppression receiver for TH-UWB wireless systems is proposed. It consists of selecting the first strongest multipath components using an appropriate Rake receiver with the path diversity combining being based on the minimum mean square error criterion. Pulse position modulation and pulse amplitude modulation schemes are considered. The expressions of the signal-to-interference and noise ratio at the output of the selective Rake combiner, the system multi-access data rate as well as the conditional bit error rate are also derived. The impact of different parameters, such as the number of selected dominant paths, the NBI power as well as the time hopping sequence code on the system performance are studied. Results reveal that the proposed receiver can almost completely eliminate the effect of NBI. 相似文献
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Wireless spread spectrum multiple access (SSMA) using time hopping and block waveform encoded (M-ary) pulse position modulated (PPM) signals is analyzed. For different M-ary PPM signal designs, the multiple-access performance in free-space propagation renditions is analyzed in terms of the number of users supported by the system for a given bit error rate, signal-to-noise ratio, bit transmission rate, and number of signals in the M-ary set. The processing gain and number of simultaneous users are described in terms of system parameters. Tradeoffs between performance and receiver complexity are discussed. Upper bounds on both the maximum number of users and the total combined bit transmission rate are investigated. This analysis is applied to ultrawideband impulse radio modulation. In this modulation, the communications waveforms are practically realized using subnanosecond impulse technology. A numerical example is given that shows that impulse radio modulation is theoretically able to provide multiple-access communications with a combined transmission capacity of hundreds of megabits per second at bit error rates in the range 10-4 to 10-7 using receivers of moderate complexity 相似文献
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Passive optical fast frequency-hop CDMA communications system 总被引:21,自引:0,他引:21
This paper proposes an all-fiber fast optical frequency-hop code division multiple access (FFH-CDMA) for high-bandwidth communications. The system does not require an optical frequency synthesizer allowing high communication bit rates. Encoding and decoding are passively achieved by Bragg gratings, Multiple Bragg gratings replace a frequency synthesizer, achieving a hopping rate in tens of GHz. A main lobe sine apodization can be used in writing the gratings to enhance the system capacity and the spectrum efficiency. All network users can use the same tunable encoder/decoder design. The simultaneous utilization of the time and frequency domains offers notable flexibility in code selection. Simulations show that the encoder efficiently performs the FFH spread spectrum signal generation and that the receiver easily extracts the desired signal from a received signal for several multiple access interference scenarios. We measure the system performance in terms of bit error rate, as well as auto-to cross-correlation contrast. A transmission rate of 500 Mb/s per user is supported in a system with up to 30 simultaneous users at 10-9 bit error rate. We compare FFH-CDMA to several direct sequence-CDMA systems in terms of bit error rate versus the number of simultaneous users. We show that an optical FFH-CDMA system requires new design criteria for code families, as optical device technology differs significantly from that of radio frequency communications 相似文献
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为了提高扩频通信系统数据传输的有效性和安全性,提出了一种混沌映射与自编码非线性融合的思想构造扩频码方法。该方法首先将Logistic混沌序列通过改进产生的复合符号混沌序列与自编码算法输出反馈进行逻辑异或,然后与自编码序列经非线性Henon映射相融合产生高质量的复合扩频码。以混沌和自编码为基础分析了该方法的有效性,并与现有方法进行比较,提高了序列的相关性和复杂度。在DS-CDMA系统中进行仿真验证,结果表明该方法产生的扩频序列抗多径干扰能力更好,并能获得较低的扩频误码率,有利于扩频通信的需要。 相似文献
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A new double-filter receiver for spread spectrum wireless systems is presented. The receiver exploits the inherent diversity due to the small delay difference between the multipaths which may not be exploited by the conventional RAKE receiver. The bit error rate performances of both the coherent and the noncoherent detectors are analyzed and compared with the ideal RAKE receiver and the matched filter bound. We also examine the best and the worst cases of a three-path fading channel for the proposed receiver. Optimum pulse shapes under various channel conditions are designed. Implementation issues in code-division multiple access systems are discussed. The numerical results show that the proposed receiver achieves significant gains for a given spreading factor under a complexity constraint. 相似文献
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We propose code hopping - direct sequence spread spectrum (CH-DSSS) with binary phase shift-keying (BPSK) modulation to compensate for intersymbol interference (ISI) in an Ultra-wideband system. The central idea is that code hopping (CH) affects ISI amplitudes that are produced by both the cross- and the auto-correlation properties of spreading codes for codewords; not just by the latter as occurs without CH. We also propose a low complexity CH pattern search algorithm to find good CH patterns. To evaluate the performance of the CH-DSSS system, a bit error rate (BER) expression is derived for a Rake receiver by applying the Beaulieu series method. Computational results show that significant gains can be obtained by CH for both the average BER and the outage probability (e.g. a 6 dB gain in outage probability for a non-line of sight channel). 相似文献